1. Field
This disclosure relates to a polymer for an optical film, and an optical film including the same.
2. Description of the Related Art
Flat panel displays may be classified into emitting display devices that emit light by themselves and non-emitting display devices that require separate light sources. Optical compensation films such as phase difference films may be used for improving image quality of the flat panel displays.
In an emitting display device, for example, an organic light emitting display, visibility and contrast ratio may be decreased due to reflection of external light by metals such as the metal in an electrode of the display device. In order to reduce such deterioration, a polarizing plate and a phase difference film are used to prevent the external light reflected in the display device from leaking out of the display device.
In a liquid crystal display (“LCD”), which is a kind of non-emitting display device, elliptical polarization and light leakage may occur due to birefringence of liquid crystal and crossed polarizing plates in the display device, thereby decreasing contrast ratio and causing color shift. An optical compensation film may convert the elliptical polarization into a circular polarization to improve the image quality of the display device.
In order to fabricate a compensating optical film having reverse wavelength dispersion, the method of co-extruding, laminating, or copolymerizing positive birefringence resin and negative birefringence resin is typically used. Further, in order to show positive birefringence, it is known that the refractive index of a polymer should be greatest in a direction parallel to the alignment axis of the main chain of the polymer. For this purpose, side chains that are capable of being aligned in an elongation direction are substituted to the main chain of a polymer. However, the effect is insignificant. In order to effectively increase the refractive index in a direction parallel to the main chain of a polymer, it is known to cyclize the main chain of a polymer. Commercialized polymers, of which the main chain is cyclized to show positive birefringence, are cyclic olefin polymer (“COP”) and polycarbonate (“PC”). These polymers are, however, very expensive and the polymerization to obtain these polymers is very difficult.
Accordingly, a polymer for an optical film, such as a compensating film having reverse wavelength dispersion is continuously sought.